During and after many downhole wellbore operations, such as hydraulic fracturing, a controlled release of chemicals often is required. A variety of chemical treatments, e.g. acid etching, have been used to enhance hydrocarbon production in such wellbore operations. It has been a challenging job to deliver chemicals in real-time and in a controlled manner. A number of solutions have been proposed, such as the use of a fluid plug, a canister, and encapsulation. Additionally, the use of micro-coil chemical delivery has been attempted, but the turbulent flow can be problematic for the micro-coil tubing.
For example, when using micro-coil, one of the major technical challenges is coil survivability. During hydraulic fracturing operations, the micro-coil is subjected to significant fluid drag force due to the large annular flow rate between the micro-coil and the production tube or casing. This external drag force, combined with the weight of the micro-coil, can lead to premature failure/breakage of the micro-coil. This survivability issue severely limits the maximum flow rate that can be pumped during the fracturing job and also limits the maximum depth that can be reached for the chemical delivery.
Existing micro-coil chemical delivery systems have focused on isotropic metal tubes, such as stainless steel and Inconel tubes. This is a viable solution as long as the target flow rate and/or the treatment depth are relatively small. However, the micro-coil is not able to withstand large flow rates and/or placement at substantial well depths.